1. Field of the Invention
The present invention relates to a water purification apparatus and a method thereof, for purifying water with oxidization process of an organic matter(s) or compound(s) contained therein, in particular, to a water purification apparatus and a method thereof, in which the organic matter(s) in water is purified with the oxidization process by use of catalysts, including photo-catalyst, such as titanium dioxide.
2. Description of Prior Art
In processing of various kinds of water, including sewage, draining from a household, river water, lake water, water of water supply or service, in particular, as a method for removing organic matter(s) including organic chlorine compound of a surfactant, such as trichloroethylene, trihalomethane, and further harmful organic matters such as dioxin and PCB, etc., from water, which may still remained within wastewater after being highly treated or processed by removing the suspended matters therefrom, there is already known oxidization process of the organic compounds or matters contained within water to be processed (i.e., raw water) with use of the photo-catalyst. The oxidization process with use the such photo-catalyst is often used or practiced for decomposing the harmful organic matters mixed or contained within a fluid such as the water, or for disinfection thereof, and as the substance showing such photo-catalytic function is well-known the titanium dioxide, for example.
Ordinarily, particle of the titanium dioxide is dispersed into the water to be treated or processed (i.e., the raw water), and thereafter ultraviolet rays are irradiated into the raw water so as to cause a reaction of oxidization on the photo-catalyst. However, the oxidization of the photo-catalyst occurs on the surface of the particle of titanium dioxide dispersed, therefore, in order to increase an efficiency of the reaction thereof, it is important that the particle of titanium dioxide dispersed into the fluid to be processed is as small or minute as possible so as to enlarge the specific surface area thereof, thereby increasing the contact area between the particle of titanium dioxide and the fluid to be processed.
Then, such the photo-catalyst particle is separated from the fluid to be processed after the oxidization process thereof, so as to be used again (i.e., for reuse), therefore, in a case where it is applied to the fluid of a gaseous body like the air, even the particle of photo-catalyst being minute in the size thereof, the photo-catalyst particle can be separated or removed from the liquid to be treated easily, because of the difference between them in the specific gravity. However, in a case where it is applied to the fluid of a liquid such as water, the minute particle of photo-catalyst dispersed into the liquid of water is very inferior or small in the precipitation or sedimentation thereof comparing to that in the gaseous body. Therefore, in a case where the liquid such as water is processed with use of the photo-catalyst, such as the titanium dioxide, the particle of photo-catalyst is made large in the size at the cost of efficiency in the reaction. Alternatively, when the fine or minute particle thereof is used, a method of so-called a membrane separation method is applied to separate the photo-catalyst particle from the fluid after being treated or processed.
However, in a case where the particle of photo-catalyst is made large in the size, there is a drawback that an apparatus or a device itself must be large-scaled for compensating the decrease in a capacity of processing accompanying with the reduction in the reaction efficiency. Further, in the case where the above-mentioned membrane separation method is applied, there is still remained a problem that a large motive power is necessitated, in particular, in the portion where the membrane separation is performed.
Therefore, from such view point of the background as mentioned in the above, conventionally, for example in Japanese Patent Laying-open No. Hei 9-174067 (1997), there is proposed a method, wherein a minute particle of iron hydroxide and/or a minute particle of aluminum hydroxide are mixed to be muddled into the water to be processed (i.e., the raw water) in an oxidization processing vessel with the minute particle of the photo-catalyst, and is added therein a polymer coagulant after the oxidization process by irradiating the ultraviolet rays. According to such method, with a function of the polymer coagulant which is added into the water to be processed after the oxidization process, the photo-catalyst particle dispersed into the water is condensed with the particles of the minute particle of iron hydroxide and/or the minute particle of aluminum hydroxide to be separated, and the separated sludge is returned to the oxidization processing vessel again for reuse thereof.
Attached FIG. 7 is a block diagram of showing a processing apparatus according to the above Japanese Patent Laying-Open No. Hei 9-174067 (1997), and as is shown in FIG. 7, first of all, an organic pollutant contained in the raw water is decomposed and/or removed (i.e., decomposed into components, such as water and/or carbon dioxide, etc.) by the oxidization due to the photo-catalyst particle within the oxidization processing vessel or reservoir 1, in the water purification apparatus according to the conventional art. Namely, in the oxidization processing reservoir 1, there is provided an light source 2 of ultraviolet rays, thereby the particle of photo-catalyst being thrown or cast into the raw water beforehand is irradiated with the ultraviolet rays so as to cause the photo-catalytic reaction thereof. However, into the water to be processed, i.e., the raw water within the oxidization processing reservoir 1, the minute particle of iron hydroxide and/or the minute particle of aluminum hydroxide are muddled in advance. And into the water flowing out from the oxidization processing reservoir 1 is added the polymer coagulant from an injection means 20 thereof.
Here, when the polymer coagulant is added into the water flowing out from the oxidization processing reservoir 1, the minute particle of iron hydroxide and/or the minute particle of aluminum hydroxide form flock with the photo-catalyst particle dispersed into the water with the condensation function thereof, and the condensed flock formed is separated as sludge 9, separating from the water to be processed in a sedimentation separation reservoir 8 positioned in a downstream thereof. Thereafter, the sludge 9 which is separated from the water to be processed is returned back to the oxidization processing reservoir 1 so as to be added into the raw water, and is utilized for the oxidizing process with the photo-catalyst particle, again.
Namely, in the water purification apparatus and the processing method thereof, according to the conventional art mentioned above, the flock (i.e., the separated sludge 9), which is returned to the oxidization processing reservoir 1 to be reused, is released from the condensation function of the polymer coagulant, since it is decomposed by the oxidization due to the above photo-catalyst in the oxidization processing reservoir 1. As a result of this, the photo-catalyst particle and the minute particles of iron hydroxide and/or of aluminum hydroxide are free from the condensation function of the polymer coagulant, and are muddled into the water as sludge particles thereof, again, to be reused. In such the manner as mentioned in the above, the oxidizing (i.e., purifying) process is achieved with high efficiency with use of the powder of photo-catalyst, in the oxidization processing method of the water according to the conventional art (i.e., Japanese Patent Laying-Open No. Hei 9-174067 (1997)).
However, there are still remained several problems with the water purification apparatus and the method thereof according to the conventional art.
Namely, there is a problem as one of them that, since the minute particle of the photo-catalyst is continuously separated and collected from the water to be processed, also the polymer coagulant must be added continuously, such as polyacrylamide, etc., being expensive in the price thereof. Therefore, it has a drawback that the cost for the apparatus becomes to be large, in particular in running cost thereof.
Further, with the water purification apparatus and the method thereof according to the conventional art, the polymer coagulant, which is added for condensing the minute particle of the photo-catalyst when the water to be processed flows out from the oxidization processing reservoir 1, is thereafter returned back to the oxidization processing reservoir 1 again, and is decomposed by the photo-catalytic reaction of the minute particle of the photo-catalyst therein. However, the energy (i.e., the ultraviolet rays) which is necessary for decomposing the polymer coagulant turned back to the oxidization processing reservoir 1 is in excess, from a view point of energy consumption which is used for decomposing the organic matter(s) in the raw water, i.e., the inherent purpose of the apparatus, thereby bringing about an ill influence upon the efficiency of the oxidizing process in the apparatus.
Furthermore, in the above oxidization processing reservoir 1, the minute particle of the photo-catalyst thrown into the raw water keeps to form relatively large condensing flocks due to the condensation function of the polymer coagulant, during the period until when the returned polymer coagulant is decomposed by the photo-catalytic reaction. Therefore, there is a problem that the photo-catalytic reaction in the oxidization processing reservoir 1 is decreased down in the efficiency thereof, since the effective contacting area of the photo-catalyst comes to be small.